<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        var year = prompt("请输入年份");
        year = parseInt(year);
        if (isNaN(year)) {
            alert("输入错误");
        } else {
            if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
                alert("闰年");
            } else {
                alert("平年");
            }
        }
    </script>
</body>

</html>